1. Field of the Invention
This invention relates to alloys, and more particularly, to a novel gold-based alloy containing gold, silver, copper, zinc, silicon, iron, boron and indium which has high resistance to cracking, improved color consistency and increased ductility for use in the manufacture of jewelry.
2. Statement of the Known Prior Art
Gold based alloys containing gold, silver, copper, iron and zinc are known to be suitable for use in the manufacture of jewelry. The proportions of constituents, such as silver, copper, iron and zinc, will vary in accordance with the purposes for which the alloy is to be used, to optimize certain metallurgical properties, and/or to obtain a desired color. U.S. Pat, No. 2,141,157 issued to Peterson is directed towards alloy compositions for the manufacture of gold articles consisting of about 33% to 84% gold, 10.7% to 67% copper, 0.1% to 5% cobalt, 2% to 10% silver and 2% to 10% zinc.
U.S. Pat. No. 2,248,100 issued to Loebich is directed towards alloys containing 33% to 60% gold, 10% to 55% copper, 0.5% to 25% zinc, 1% to 30% silver and 0.1% to 5% iron.
U.S. Pat. No. 2,229,463 issued to Leach discusses gold alloys consisting of 35% to 75% gold, 5% to 25% silver, 12% to 35% copper, 0.1% to 12% zinc and 1% to 5% iron.
However, each of these known alloys have not solved the typical problems associated with gold based alloys. Gold-base alloys, heretofore commonly used for making jewelry articles from sheet and wire, frequently develop the defect known as "orange peel" when the alloy is alternately subjected to stress at a high temperature and mechanical working at room temperature. This defect is due to a coarse grain structure and is characterized by surface roughness similar in appearance to the outer surface of the skin of an orange. This appearance is objectionable because a smooth even lustrous surface, normally required in finished gold jewelry, becomes difficult or impossible to obtain. It is particularly objectionable when it develops on the gold alloy clad layer of rolled gold plate. Mechanical shaping often produces this deformation which often results in exposing the base metal substrate.
Other difficulties encountered with known gold based alloys are the variations in color and surface texture form the construction of jewelry using investment cast and stamped components. Since components stamped from rolled sheet stock generally are of a different color than investment cast parts due to the compositional differences necessary to obtain certain physical properties required for mechanical stamping which may be unsuitable for investment casting techniques. Therefore, multicomponent jewelry usually requires electroplating following basic construction in order to obtain a single uniform color and texture throughout.
Another of the difficulties encountered in the manufacture of clad gold articles of jewelry is the provision of a gold plate which will stand up against the abrasion caused by clothing, etc. The gold plate of such an article is generally very thin, and the life of a clad gold article is determined to a great extent by the resistance to abrasion of the gold plate. It is known to provide gold alloys of a given karat with metals of harder nature to withstand wear. The effect on the gold alloy is to give greater hardness, but the resulting color and required ductility, from the standpoint of the jewelry industry, is not as good as softer alloys. Consequently, it has been a problem to provide a hard gold alloy in a given karat which produces a color and grain structure acceptable to the jewelry industry.
In order to obtain high quality investment castings certain elements (e.g. silicon) must be added to provide smooth shinny surfaces and limited remelting capabilities. Silicon bearing alloys normally are unsuitable for sheet rolling and wire drawing. Sheet and wire alloy preparations often use phosphorus as a deoxidant which causes a dull, discolored surface on investment cast jewelry.
In the manufacture of many articles of jewelry, either the goldclad variety or the solid karat gold variety, it is necessary many times in the course of manufacture, to submit the article to either high annealing temperatures or high soldering temperatures. Known gold alloys of similar color have softened unduly with either of these treatments, causing distortion and too great flexibility in the finished article. This condition may create excessive wear after use. This is caused by softness in the finished article caused by many necessary annealing operations during the manufacturing process.